The invention relates to a process and an apparatus for examining optical components, in which an image of the particular component to be examined is produced and flaws in the imaged article are detected by image analysis, and furthermore to an illuminating device for illuminating clear-transparent test objects.
In the manufacture and quality control of optical components, especially optical components for the eye, such as contact lenses, examination is still carried out visually. Attention may be drawn in this connection, for example, to DIN specification 58 223. Visual quality control is a subjective examination only, which depends on the person concerned and is likely to vary depending on the time of day. Consequently there are inevitably shifts in the quality standards of the quality control and it is not possible to achieve adequate reproducibility of the quality of the products. In addition, the possibilities of automation, especially where such components are mass-produced, are considerably handicapped.
Detection of the presence or absence of scratches and the like on the curved surface of lenses in contact lens manufacture by means of an optical projector device and an image-processing device is known from EP O359 084 A2. The said specification does not, however, disclose how the projector device and the image-processing device are designed so that they can be used for a reproducible quality control, especially in the automatic production of optical components.
Referring to illumination of test objects, the illumination of objects in a microscope by means of "dark field illumination" is known. Such a dark field illumination comprises illuminating an object by means of a light source and an illuminating lens (condenser) in such a manner that the illuminating light beam does not itself enter the ray path of the microscope. Consequently, only the light that is scattered into the ray path by the object is observed.
Illuminating lenses for dark field illumination are known in which there is arranged in the ray path a central diaphragm plate which covers the central portion of the illuminating light beam. It is thus an annular illuminating light beam which strikes a condenser lens and which is collected by the edge parts of the condenser lens in the plane of the object and then directed to the side past the ray path of the microscope lens.
Also known is a so-called "cardioid condenser" in which an annular illuminating light beam is fully reflected at a concave surface at the object side of a first lens. The light beam deflected outwards in this manner strikes an essentially cylindrical generated surface of a second lens. The light beam is again fully reflected by this generated surface. The second lens collects again in the plane of the object the light beam reflected inwards from the edge. From there the light beam, in the shape of a cone, again passes by the ray path of the microscope (Grimsehls Lehrbuch der Physik, 11th edition (1943), vol. 2, published by B. G. Teubner, pages 707-708). These known arrangements are concerned with the illumination of objects in a microscope having an invariable illuminating lens.